Recent advances in the systematics and phylogeny of Mediterranean groups of Boraginaceae
F. Selvi, L. Cecchi, A. Coppi
Introduction - Taxonomic problems in family Boraginaceae s.l. range from the level of order to that of species and below, mainly due to the still largely incomplete knowledge of many groups and to the difficult interpretation of shared characters as phylogenetically informative homologies or rather as simple analogies.
Based on recent molecular phylogenetic analyses, there is evidence that Boraginaceae, as traditionally treated, is a paraphyletic group also including Hydrophyllaceae and Lennoaceae. To avoid paraphyly, it either has to include these two well-established families at subfamily rank or, alternatively, the traditional subfamilies Cordioideae, Ehretioideae, Heliotropioideae and Boraginoideae must be elevated to family rank. Such a second taxonomic option is preferrable, in order to have a monophyletic order Boraginales consisting of six natural families: Cordiaceae, Ehretiaceae, Heliotropiaceae, Hydrophyllaceae, Lennoaceae and Boraginaceae s.str. Position of Boraginales is within the Euasterid-I clade of the APG, and possibly sister to Solanales, Gentianales and Lamiales.
Intended in a narrow sense, Boraginaceae consists of at least five tribes, Lithospermeae, Boragineae, Cynoglosseae, Eritrichieae and Echiochileae, plus two still ill-defined groups, Trigonotideae and Trichodesmeae.
The spine of the family phylogeny as resulting from the few molecular studies published to date suggest that Boragineae, Lithospermeae and Echiochileae are monophyletic groups, while the genera of Cynoglosseae and Eritrichieae seem to form a broad paraphyletic complex in which distinction of the two tribes as established on a traditional morphological basis can not be clearly recognized. The focus of our research in the last years has been the systematics and phylogeny of tribes Boragineae and Lithospermeae. Taxonomic problems in these groups are historically at the genus level.
Boragineae - Boragineae are exclusive to the Old-World and comprise 15 genera some of which of difficult circumscription. A molecular phylogenetic study using the plastid trnL(UAA) intron and the nuclear ITS1 region has supported the monophyly of the tribe and an early split into two main clades, the sister of which is the western-european monotypic genus Pentaglottis. The first clade consists of the three lineages Pulmonaria-Nonea, Borago-Symphytum and Brunnera.
Nonea-Pulmonaria - We have recently investigated in detail the relationships in the critical Pulmonaria-Nonea lineage, in order to arrive to satisfactory generic delimitations. Our phylogeny shows that: 1) the eastern Mediterranean species Nonea obtusifolia is sister to the rest of the ingroup and outside either Nonea or Pulmonaria; 2) Nonea/Elizaldia and Paraskevia/Pulmonaria are sister groups; 3) Nonea as currently circumscribed is paraphyletic because Elizaldia is firmly nested inside it; 4) the critical monotypic genus Paraskevia is closely related to Pulmonaria. Combined with morphological, karyological and chorological aspects, there is strong support for: (i) the institution of a new monotypic genus (Melanortocarya) for N. obtusifolia, (ii) the inclusion of Elizaldia within Nonea, and (iii) the inclusion of Paraskevia in Pulmonaria.
Borago - In the Borago-Symphytum clade we have investigated the phylogeny of Borago in relation to karyotype variation and evolution and cytogeography of endemic subgenus Buglossites in the Corso-Sardinian microplate.
Chromosome variation in Borago is wider than previously known, with four base numbers, x
= 6, 8, 9 and 15, and three ploidy levels based on x = 8. In subg. Buglossites the Sardinian endemic B. morisiana is diploid with 2n =18, while B. pygmaea includes three allopatric cytotypes with 2n =30 (Sardinia), 2n =32 (southern Corsica) and 2n =48 (central northern Corsica and Capraia). In subgenus Borago, the Moroccan endemic B. trabutii and the
widespread B. officinalis have 2n =12 and 2n =16, respectively. Two base numbers may represent the ancestral condition in this small genus, x =6 or x =8. Increase in chromosome number and karyotype asymmetry, a decrease in chromosome size and heterochromatin content, and the appearance of polyploidy are the most significant karyological changes associated with the divergence of Buglossites. High ITS1 variation in the tetra- and hypotetraploid races of B. pygmaea suggests a multiple origin, while the lower polymorphism of the hexaploid race and its allopatric distribution in northern Corsica and Capraia is better explained with a single origin via union of unreduced and reduced gametes.
Anchusa s.l. - The second main clade of the Boragineae corresponds to the well-supported group of Anchusa s.l., with monotypic genus Trachystemon as sister taxon. Anchusa s.l. is highly paraphyletic to its small, segregate genera Phyllocara, Hormuzakia, Gastrocotyle, Cynoglottis, Lycopsis and Anchusella. These morphologically well-characterized, segregate genera are all supported by DNA sequences and should be definitively accepted. Also the subgenera of Anchusa s.s. (Buglossum, Buglossoides, Buglossellum) are all supported as monophyletic groups by DNA data, in spite of their weak morphological characterization with respect to Anchusa s.str. The only exception is Anchusa subgenus Limbata which is nested in A. subgenus Anchusa despite marked divergence in floral morphology. A more natural classification will be required in the future if other markers will confirm such a paraphyly of Anchusa s.str. Species relationships within Anchusa s.str. are poorly resolved due to the low rate of molecular variation. This appears in contrast with both the morphological differentiation between species and with the infraspecific phenotypic polymorphism of several taxa, suggesting a recent history of rapid and partly adaptive radiation in the Mediterranean and continental Europe. The only exception is given by the endemic Sardinian taxa, which show a weak divergence with respect to the rest of Anchusa. We wanted therefore to investigate in greater detail the origin and the relationships of the six endemovicariant taxa of the Corso-Sardinian microplate, adding AFLP fingerprinting to the ITS phylogeny. AFLP provide a finer level of resolution, as well as reliable estimates of within-population genetic diversity and among population genetic distances; these data are also important for planning conservation actions of these extremely vulnerable island endemics. ITS phylogeny of the whole group suggests that the three orophytic taxa A. formosa, A. capellii and A. montelinasana form a clade sister to the psammophytic coastal endemics A. crispa, A. littorea and A. sardoa, but preliminary AFLP data fit only in part in this picture.
Lithospermeae – This group is represented by ca. 24 genera in both the Old and New world, 18 of which are represented in the Euro+Med region. In the total lack of modern phylogenetic studies, relationships and generic limits are in some cases still tentative. We are using morphology and karyology combined with nuclear ITS and plastid matK DNA sequences to open a window on the phylogeny of the old-world genera of the tribe. At this moment, the obtained trees (16 genera sampled) form a grade in which most of the currently accepted genera seem to be resolved. Of particular interest is the position of Halacsya and Paramoltkia, two remarkable monotypic genera endemic to the Balkan serpentine outcrops. Also in view of their edaphic specialisation (obligate serpentine endemics), they have been viewed as isolated, relict taxa of very ancient origin without clear relationships within extant Lithospermeae. According to some other authors (e.g. Johnston), however, they are both close to Moltkia, a small genus of six species with some morphological affinity. This second hypothesis does not receive support from our preliminar trees, which bring to the light a considerable distance of the two genera with respect to Moltkia. Shared characters in, e.g., fruit seem to be homoplasic. Halacsya and Paramoltkia are instead sistergroups in a well supported clade, in spite of their considerable morphological “distance”. This finds support in pollen morphology, confirming the strong phylogenetic signal of palynological characters in the systematics of Boraginaceae. In a phylogenetic perspective, the obligated
serpentinophytism of Halacsya sendtneri and Paramoltkia doerfleri may represent an ecological symplesiomorphism due to common ancestry, rather than an ecological homoplasy originated independently in two otherwise unrelated lineages. The clade Halacsya/Paramoltkia belongs to a larger group also including the monotypic genera Mairetis, Molkiopsis and Neatostema, but not Moltkia. The latter has possibly closer relationships with the Lithospermum/Buglossides clade and contains two well distinct subclades corresponding to the West Asiatic subgenus Moltkia (M. aurea and M. caerulea) and the South European subgenus Echianthus (M. petraea and M. suffruticosa).
Cerinthe - At the species level, we are finally investigating the systematics and phylogeny of genus Cerinthe. Preliminary trees show that the genus is split in two well supported lineages, one of species with 2n = 18, including all species of subg. Ceranthe, and one of taxa with 2n = 16, mainly corresponding to the C. major s.l. group (subg. Cerinthe) The ancestral forms of the the genus are possibly found in subgenus Ceranthe, and possibly within the perennial group of C. glabra distributed in south European mountains. The rare Corsican endemic C. tenuiflora, doubtless a good species, is sister to the all the other taxa and is well distinct from the continental C. glabra, of which it is currently considered a subspecies. The annual group of C. major has instead derived characters. Descending aneuploidy (2n = 18 → 2n = 16) paralleled by a shortening to the life-cycle (perennial → annual) as adaptive response during radiation in dry habitats, is known to occur elsewhere in Boraginaceae (e.g. Nonea). Psammophytic Cerinthe oranensis (N Africa) is sister to C. major, which includes the variant subsp. gymnandra. Work on this genus is still in progress, with the analysis of C. smithiae, C. retorta, C. tristis and C. palaestina.
Conclusion: recommendation of the genera of Boraginaceae to be recognised in the forthcoming Euro+Med project.
